I started getting some seriously annoying vibration noise at idle from the back - and peeking underneath, I see that my muffler is rusted - and separating? There's like a second skin on the muffler that is all rusted and peeling off. Is there harm in just removing it, or is this something I should just replace? Seems like there is a fine, yet rusty looking, muffler inside...

Separating muffler?

 

I'd replace the muffler. If the outer skin (heat shield?) is rusted out I have to question how intact the actual muffler is.

A tech would probably use a smoke machine to check for exhaust leaks. Even if none the heat shield removed presents a risk of fire.

 

Mine was very similar to yours; I made the decision to replace it.

 

Thanks guys. I agree now that i think about it. Probably best to go ahead and get it replaced.